With international tests showing that the United States no longer leads in school achievement, a bipartisan coalition of reformers is advocating the creation of more charter schools and a system of basing pay and firing decisions for teachers on students' standardized test scores. Conservatives have long recommended such businesslike approaches for schools, and Republican lawmakers and politicians are pushing for laws to weaken unions' ability to defend teachers against charges of incompetency. Teachers' unions remain opposed to market-oriented reforms, but the philosophy has new adherents among education-reform groups and centrist Democrats such as President Obama, whose administration is providing funding to states to develop data-driven teacher assessments. Meanwhile, some education scholars point out that poorly performing students are concentrated in low-income districts, where funding shortfalls, bad teaching conditions and poverty make educating students more difficult.